1. Field of the Invention
This invention relates to a thin film multi-junction photovoltaic array module of solar electric concentrator power systems.
2. The Prior Art
During the 1990""s most photovoltaics with flat plates of silicon solar cells produced electricity at a conversion efficiency of between 15% to 18% of that of commercial market systems. Since then, the Department of Energy and the PV manufacturing industry has substantially improved thin films and multi-Junction solar cells. In 1999, Spectrolab broke the world record when it produced new triple-junction solar cells with a known commercial efficiency of up to 34%.
The fact that the new triple-junction solar cells cost much more than conventional solar cells made it impossible to design photovotaics with flat plates to be solar receivers for electricity production.
U.S. Pat. No. 5,505,789 to Fraas et al discloses a line-focus photovoltaic module using solid optical secondaries for improved radiation resistance. This invention consists of an array of linear arched fresnel lenses with a linear photovoltaic cell receiver located along the focal line of each lens. The optical secondaries may be parabolic in shape.
These systems disclose the combination of fresnel lenses, and parabolic reflectors. U.S. Pat. No. 6,384,320, the disclosure of which is herein incorporated by reference, discloses a combination of a fresnel lens, compound parabolic reflector incorporated with third optical concentration glass lenses and multi-junction solar cells for photovoltaic electric energy conversion.
A low-cost, high-efficiency, concentrator was designed to be coupled with a much smaller area of expensive solar cell with point focus. The solar electric concentrator is a combination of fresnel lens and optical reflectors which can concentrate solar intensity 300 to 1000 times within a six-inch distance. The solar electric concentrator can be made from low cost, conventional material, and replaces large portions of a module""s surface area because its point focus needs a smaller area of expensive solar cells.
The invention relates to a thin film multi-junction photovoltaic array module of solar electric power generation systems. The high performance photovoltaic (PV) array module has multi-junction concentrator solar cells that convert received solar energy to electricity.
A photovoltaic solar cell is a semiconductor device that converts sunlight directly to electricity through the Photovoltaic Effect. One of the important developments of PV applications is the lowering of the system cost through the design of the PV array module to more efficiently convert the sunlight directly to electricity.
The PV array module contains multi-step concentrations of sunlight with Fresnel lenses, CPC reflectors and specially shaped glass lenses that can be made with much smaller surface areas of expensive multi-junction concentrator solar cells in the system. Solar high-concentration and high-efficiency multi-junction solar cells are the essential factors for lowering the cost of PV array modules which produce electricity.
The concentrator has two layers of fresnel lenses concentrating sun rays twice. The second fresnel lens refracts the incoming rays an additional 30xc2x0. This larger refraction adds four hours of useful time to the system. The CPC is also readjusted to trap more than eight hours daily of direct-beam solar irradiation. The photovoltaic module tracking device which follows the sun can be eliminated from a solar electric power system. Therefore, the total cost of the whole solar electric system can be reduced by 30%. With this modification, it becomes commercially possible to install the low-cost, high-efficiency stationary concentration photovoltaic solar electric generation systems on the roof of a building or a fixed frame, and connect it to the power grid on a utility scale.